The present invention relates generally to methods and apparatus for decoding digital video or motion picture signals and, more particularly, to video error concealment for block-based video decompression.
Video decompression of compressed signals is applicable in static recording media such as optical discs (e.g., DVD and VCD), in broadcast (e.g., via network), in streaming media (e.g., WMV and real video), and the like. Examples of video compression include MPEG (Moving Picture Experts Group) 2 and MPEG 4. In the MPEG systems, differences between pictures of the motion picture signal are determined to reduce redundancy in the time domain. These differences are subject to a discrete cosine transform (DCT) to reduce the redundancy in the spatial domain. Generally, a digital video signal coding apparatus first performs motion compensation for each of the pixel blocks (e.g., N×N pixels) which constitute the previous frame in order to remove correlation in time, and calculates a difference value of each pixel block between the previous frame and the current frame. The amount of information relating to the difference values is much smaller than the amount of information relating to the current frame. The difference values and motion vectors used for the motion compensation are coded, and binary codes are outputted. A digital video signal decoding apparatus decodes the binary codes outputted from the coding apparatus to obtain a difference value of each pixel block between the motion-compensated previous frame and the current frame, and a motion vector used for the motion compensation for that pixel block. The decoding apparatus has a frame memory for storing the previous frame. Pixel blocks that constitute the previous frame stored in the frame memory are motion-compensated by using corresponding motion vectors. The difference values are added to the motion compensation pixel blocks in the previous frame to reproduce the current frame. The reproduced current frame is then stored in the frame memory. In this way, the decoding apparatus allows the current frame to be reproduced only by the use of the difference values of the respective pixel blocks between the previous frame and the current frame, and the motion vectors.
If the compressed motion picture signal includes an error which cannot be corrected by the error correcting ability of the decoder, the resulting motion picture output signal lacks a portion corresponding to the erroneous part of the compressed signal. An error concealment mechanism is needed to ensure that the missing signal portion does not noticeably impair the quality of the picture displayed in response to the motion picture output signal.